1. Field of the Invention
The present invention relates to a semiconductor device comprising a semiconductor chip having bump electrodes thereon. The present invention relates also to a manufacturing process and an inspecting method of the semiconductor device.
2. Description of the Prior Art
Electronic apparatuses such as a mobile information terminal have been made smaller and lighter in recent years. Accordingly, demands for a smaller and lighter semiconductor integrated circuit device (hereinafter semiconductor device) for use in such electronic apparatuses have been growing. One of popular methods for making the semiconductor device smaller and lighter is to form so-called bump electrodes at predetermined spots on a surface of the semiconductor device. Then, the semiconductor device is mounted on a printed circuit board through the bump electrodes together with other electronic components.
In practicing the above-mentioned method, it is important that all of the bump electrodes should be formed on a semiconductor chip without missing any one of them. A failure to do so would lead to a defective semiconductor device as a whole, because, if a semiconductor chip having a partially missing bump electrode is mounted on a semiconductor device due to a trouble or the like during a process of forming the bump electrodes, a proper electrical connection is not achieved between the semiconductor device and a conductor pattern formed on the printed circuit board.
Usually, visual inspections are conducted in many cases when the bump electrodes formed in the semiconductor device are checked because a missing or incomplete bump electrode can not be detected by a wafer test alone. This is because, in a conventional semiconductor device, a bump electrode is so formed as to make a contact with a pad through an opening formed on the pad in a surface protective film that is laid on the semiconductor chip. As the opening is larger than a diameter of a probe needle used for the wafer test, the probe needle detects identical electrical characteristics during the wafer test performed after forming the bump electrode regardless of whether the bump electrode is complete or incompletely.
In other words, when the bump electrode is properly formed, electrical continuity is achieved between the probe needle and the pad through the bump electrode. When the bump electrode is missing, the probe needle penetrates through the opening and comes in contact with the pad directly. As a result of this, electrical continuity is achieved between the probe needle and the pad, and identical electrical properties are detected as is the case for the properly formed bump electrode.
In this case, because electrical continuity is achieved between the probe needle and the pad regardless of whether the bump electrode is completely or incompletely formed and the electrical characteristics test during the wafer test does not reflect the existence of the incompletely formed bump electrode, the wafer test can not detect the missing bump electrode. This causes necessity of the visual inspection as described previously.
However, as a wafer diameter becomes larger and a semiconductor device increases its performance and features, a number of input and output terminals on the semiconductor device has been phenomenally increased. As a result, this has made the visual inspection practically impossible. Although there are automated inspection apparatuses using an image recognition system to inspect the bump electrodes for incomplete formation thereof or the like, these apparatuses are expensive and, therefore, can not be easily put into use.
As one example of conventional semiconductor devices that make detection of incomplete bump electrodes possible without requiring any special apparatuses, Japanese Patent Application Laid-Open No. 2000-21939 discloses a semiconductor chip and its inspecting method, wherein electrode terminals for inspecting bump electrode formation are formed on the semiconductor chip and existence of the incomplete bump electrode is detected by measuring electrical characteristics on the electrode terminals.
FIG. 10 shows a simplified plan view of a semiconductor chip 100 mounted in the semiconductor device disclosed in Japanese Patent Application Laid-Open No. 2000-21939.
In a configuration shown in FIG. 10, 116 is a bump electrode and 113 is a pad for external connection. Also, electrode terminals 101a to 101d for inspecting bump electrode formation are arranged along edges of corners of the semiconductor chip 100. When results obtained by measuring the electrode terminals 101a to 101d are not equal to desired characteristics, it is concluded that the semiconductor chip is defective as having an incomplete bump electrode.
According to the above-mentioned disclosure, it is assumed possible to find, without relying on visual checking conducted manually, whether the semiconductor chip 100 is defective or not through detecting incomplete formation of the bump electrode automatically. Therefore, it is assumed also possible to reduce time required for visual checking conducted on the semiconductor chip after the wafer test and to contribute to reducing production cost of semiconductor chip comprising the bump electrodes.
However, in the configuration disclosed in Japanese Patent Application Laid-Open No. 2000-21939 as shown in FIG. 11, the semiconductor chip 100 has the bump electrodes among which only about 90% are completely formed, because the semiconductor chip 100 is taken from a perimeter area of the wafer. According to this configuration, incomplete bump electrodes formed at around the corners of the semiconductor chip 100, for example, an incomplete bump electrode formed in an incomplete bump area 102, can be detected. However, an incomplete bump electrode formed in different areas than the areas in which the electrode terminals 101a to 101d are provided, in other words, an incomplete bump electrode formed in areas other than the corners can not be detected.
Because a semiconductor chip having an increased number of terminals has a higher probability of having the bump electrodes being incompletely formed in areas other than four corners, conventional semiconductor devices including those disclosed in Japanese Patent Application Laid-Open No. 2000-21939 may not be easily checked for incomplete bump electrodes that are supposed to be formed in any given areas or in any other areas than the four corners. Therefore, it may be possible that the semiconductor devices with incomplete bump electrodes are shipped. Consequently, this contributes to reducing reliability of said semiconductor devices.
An object of the present invention is to provide a semiconductor device, its manufacturing process, and its inspecting method by which a bump electrode formed improperly in the semiconductor device is detected by simple means without using a specially arranged apparatus.
To achieve the above object, according to the present invention, a semiconductor device comprises a semiconductor chip, a pad formed at a predetermined location on a surface of the semiconductor chip, a surface protective film formed on the surface of the semiconductor chip except on a part of a surface of the pad, an opening portion left in the surface protective film on said part of the surface of the pad, and a bump electrode formed through the opening portion so as to contact with the pad, wherein said opening portion comprises one or a plurality of openings having a width thereof smaller than a predetermined value, the opening has a first opening end at a side of the pad and a second opening end at a side opposite to the first opening end, and one width of an overlapping area formed by projecting the first opening end and the second opening end in a direction normal to the surface of the pad is smaller than a tip diameter of a probe needle for measuring electrical characteristics of the semiconductor device.
In the semiconductor device, the opening is arranged in a grid pattern or a stripe pattern.
In the semiconductor device, the opening is formed along a normal line to the surface of the pad or is formed with an inclination to a normal line to the surface of the pad.
According to another aspect of the present invention, a process of producing a semiconductor device comprises forming a pad at a predetermined location on a surface of the semiconductor chip, laying a surface protective film on the surface of the semiconductor chip except on a part of a surface of the pad, and forming a bump electrode through an opening portion left in the surface protective film on said part of the surface of the pad so as to contact with the pad, wherein, when the surface protective film is laid, said opening portion is so formed to have one or a plurality of openings, each having a first opening end at a side of the pad and a second opening end at a side opposite to the first opening end, so that one width of an overlapping area formed by projecting the first opening end and the second opening end in a direction normal the surface of the pad becomes smaller than a tip diameter of a probe needle for measuring electrical characteristics of the semiconductor device.
In the process, the opening is arranged in a grid pattern or a stripe pattern.
In the process, the opening is formed along a normal line to the surface of the pad or is formed with an inclination to a normal line to the surface of the pad.
According to still another aspect of the present invention, a method for testing a semiconductor device having a pad formed at a predetermined location on a surface of a semiconductor chip, a surface protective film laid on the surface of the semiconductor chip except on a part of a surface of the pad, and a bump electrode formed through an opening portion left in the surface protective film on said part of the surface of the pad so as to contact with the pad, the method including bringing a probe needle for measuring electrical characteristics of the semiconductor device in a direction substantially normal the surface of the pad so that the probe needle comes in contact with the semiconductor device, wherein the method comprises detecting the bump electrode as defective if the bump electrode is incompletely formed and an electrical contact between a tip of the probe needle and the pad is prevented by the opening portion so formed as to have an opening of which one side is smaller than a tip diameter of the probe needle.